An analytical procedure for analyzing a sample mixture requires sample preparation, which transforms a sample from its raw state into an ideal format for subsequent analysis using analytical techniques, such as high performance liquid chromatography (HPLC), ultra high pressure liquid chromatography (UPLC), HPLC or UPLC coupled with mass spectrometry (MS) or tandem mass spectrometry (MSMS), or gas chromatography (GC) coupled with MS or MSMS.
The term “sample” used in this application refers to any mixture or suspension or solid which an individual desires to analyze. The term “mixture” is used in the sense of a fluid containing one or more compounds of interest and unwanted interferences. The term “suspension” refers to a fluid in which particles or solids are held. The fluid may comprise water and/or other liquids and gases. A compound of interest is referred to as an analyte. The term “sample preparation” used herein refers to a process which involves a series of steps to extract or isolate analytes or compounds of interest from a sample mixture.
There are many extraction techniques such as centrifugal separation, filtration, liquid-liquid extraction, solid phase extraction, etc. Among them solid phase extraction (SPE) is one of most widely used sample preparation techniques for last two decades.
A SPE device typically comprises filters for filtration and separation media for chromatography. The term “filter” refers in the broadest sense to any device containing a porous material which can remove or block particles or solids held in a sample mixture or suspension passing through the device. For example, without limitation, a filter can be a membrane, a screen, or a frit. The term “separation media” refers to particles, porous monolith materials, and the like known in the art.
A SPE process typically involves steps of filtration and chromatography. Filtration and chromatography are separation methods for extracting or isolating one or more compounds or solids found in a mixture.
Filtration separates or isolates materials due to size. Particles and solids which have size dimensions which exceed the size of pores, channels, passages or openings of filters such as screens, frits, membranes and the like will not pass through.
Chromatography separates or isolates compounds due to the differences in affinity one compound has to the mixture in which it is dissolved and to another phase as the mixture and the other phase move in relationship to each other. Normally the mixture, sometimes referred to as the mobile phase, moves in relationship to a packed bed of particles or a porous monolith structure, referred to as the stationary phase.
Though SPE is viewed as one of most efficient, time-saving, and dynamic sample preparation techniques for decades, depending upon sample complexity, a SPE process can take from a few minutes to several hours. Further, a typical SPE process involves transferring a sample material from one container to another a number of times; this obviously increases the chance of losing analytes in a sample and thus sacrifices sensitivity.
It would be desirable to have a standardized SPE device and a standardized SPE method, by which a sample preparation process from beginning to end can be carried out in one place or container, such that less time is required to transform a raw sample from its original state to an ideal format, and such that less samples amount is required to achieve the same level of sensitivity.
It would also be desirable to use existing common laboratory equipments to effect sophisticated separations based on the affinity for or against a solid phase separation media or filters to isolate low concentration analytes from large volumes of solution.